Process for the hydrogenation of steam cracked naphtha



Unite ABSTRACT OF THE DISCLOSURE A process for hydrogenation of a steam cracked naphtha with a sulfided nickel-tungsten catalyst under critical conditions of temperature, pressure, space velocity and hydrogen to naphtha ratio.

This invention relates to a process for the hydrogenation of steam cracked naphtha. More particularly, the invention relates to a process for the hydrogenation of steam cracked naphtha having a very high bromine number at critical conditions which make such a process feasible.

In recent years, the steam cracking process has become increasingly popular as a source of ethylene and other olefin gases. Feedstocks ranging from light hydrocarbon gas to gas oil and heavier fractions are passed with steam through a high temperature pyrolysis furnace where cracking takes place. The process is designed and operated to produce a maximum amount of ethylene and propylene. However, a steam cracked naphtha or pyrolysis gasoline is produced in amounts ranging from 125%, depending on feed characteristics and operating conditions. Typical commercial processes are described in Hydrocarbon Processing. November 1965, vol. 44, No. 11, pp. 203-208.

Steam cracking is also employed to produce acetylene or a mixture of acetylene and ethylene. This process also produces a quantity of pyrolysis gasoline. Commercial processes for the production of acetylene and mixtures of acetylene and ethylene are described in the previously cite-d publication at pages 165 and 166.

The raw pyrolysis gasoline from steam cracking is treated to remove unstable mate-rials, to improve odor and to improve octane sensitivity, usually by heat soaking or hydrogenation in one or more stakes. When the feed to the steam cracking process is one of the heavier feeds, such as gas oil or crude oil, the pyrolysis gasoline I is extremely unstable. At conventional hydrogenating conditions, the catalyst bed rapidly plugs with polymer. Heat soaking is not suitable because the treated gasoline is still too unstable for use as a blending component in finished gasoline. Multistep hydrogenation processes are too expensive and complicated.

The object of this invention is to provide a feasible process for hydrogenating extremely unstable pyrolysis gasoline. I have found that the desired hydrogenation can be carried out over long periods employing a sulfided nickel-tungsten catalyst and critical hydrogenation conditions.

The benefits obtained from the process of the invention will be illustrated by the following description and examples.

As stated previously, the feed is a highly unstable byproduct naphtha recovered from the steam cracking of a petroleum hydrocarbon material. The feed is characterized by a boiling range of F. to 475 PI, preferably 100 F. to 430 F., a high content of olefins and diolefins, -i.e., from 30 to 50 wt. percent, and correspondingly a high bromine number of 50 to 135 cg./g. Steam States Patent 0 "ice cracking feeds having a major proportion (90-100%) of hydrocarbons boiling in the range of 3001200 usually 4001000 R, are the sources of these unstable pyrolysis naphthas. A material of particular interest is gas oil boiling in the range of from about 400 F. to about 750 F. Very large quantities of gas oil are available in certain areas for steam cracking and with the steadily increasing size of steam cracking units it can be seen that an effective treating process must be available to render large amounts of pyrolysis gasoline suitable for use as a motor fuel component.

The raw feed to the process is so unstable that some of it polyme-rizes on standing and it may be necessary to remove polymer by any appropriate means. If desired, fresh stock may be mixed with some polymerized (aged) stock and/or with recycled product.

Any suitable reactor can be used for the process. The reaction is usually started by flowing the hydrogen containing gas through the reactor to obtain the desired temperature in the catalyst bed, then adding the steam cracked naphtha. Any suitable hydrogen-containing gas having a hydrogen content of to 100% H can be used.

The catalyst is nickel-tungsten on an inert support such as alumina, keiselguhr, silica-free clay, bauxite, .mullite, etc. Alumina is the preferred support. The catalyst contains from 4 to 6 wt. percent nickel, 14 to 20 wt. percent tungsten, and the balance alumina. The tungsten to nickel ratio is preferably 4 to one to 5 to one. The catalyst is sulfided with H S or CS prior to use. The most popular catalyst for hydrogenation reactions is cobaltmolybdate on alumina. However, the examples will show that this catalyst is not acceptable for use in the process of the invention.

The feed use-d in the following examples was a steam cracked naphtha obtained from the steam cracking of a gas oil. This naphtha had the following inspection data:

Specific gravity at F. 0.824 13? F.) 114 End point F.) 418 Gum existent (mg/ ml.) 620 Copper beaker gum (mg/100 ml.) 1003 Bromine No. (cg./g.) 103.5

TABLE I [0 /400" F. Overhead Cuts with 25 lbs/1,000 B Phenylenediamine iibitor] Run No.

Feed Catalyst Cobalt N iclrel-Tungsten on Molybdate Alumina on Alumina Temperature, F 300 300 300 300 Pressure, p.s.i.g 800 800 800 800 Space Velocity (v.lhr./v.) 1.0 1.0 1. 3 1. 6 Treat Gas:

s.c.f.lb 1,000 1,000 1, 000 1,000 Percent H 70 70 7O 70 Product Data:

Yield, vol. percent". 100.0 83 87 91 92 Bromine numuer.. 70 66 81 84 Exist gum, nag/100 1111...- 100 7 3 2 2 Copper Beaker Gum,

rug/100 ml 25 11 20 29 Breakdown, miu., AS'IM D-525 30 880 560 365 Sulfur 0. 15 0. 18 0. 20 0.22 Diolefins, wt. pcrcen 16 4 1 2 5 Odor (Odor Panel) Poor Fair Good Good Good Octane Nos. plus 2 ml.

TEL/gal:

Research 97. 6 98.0 98.5 98. 7 98.2 Motor 82.0 83.4 84.1 84. 6 84.3

Table I shows that superior results are obtained with the nickel-tungsten-alumina catalyst.

It is essential that the reactor inlet temperature be maintained at less than about 300 F. Rapid plugging of the reactor bed occurred at 350 F. Operating periods of i 90 days or more can be achieved by hydrogenating steam cracked naphtha according to the process of the invention.

What is claimed is:

1. A process for hydrogenating steam cracked naphtha comprising contacting said naphtha in a reactor with a sulfided nickel-tungsten catalyst supported on an inert carrier with a hydrogen-containing gas under critical hydrogenating conditions including (1) a reactor inlet temperature ranging from about 200 F. to about 300 F., (2) a AT across the catalyst bed of from about 50 to about 200 F., (3) a pressure of 300 to 1200 p.s.i.g., (4) a space velocity of 0.25 to 2.0 v./hr./v., (5) a hy' drogen to naphtha ratio of 500 to 2500 s.c.f./b., and recovering a stable motor gasoline component.

2. Process according to claim 1 in which the boiling range of the steam cracked naphtha is 100 to 430 F.

3. Process according to claim 1 in which the bromine number of the steam cracked naphtha is at least 50.

4. Process according to claim 1 in which the steam cracked naphtha contains 30 to 50 wt. percent mono and diolefin hydrocarbons.

5. Process according to claim 1 in which the nickel content of the catalyst is 4 to 6 wt. percent and the tungsten content of the catalyst is 14 to 20 w. percent.

6. Process according to claim 1 in which the steam cracked naphtha contains 0.01 to 0.3 wt. percent sulfur.

7. Process according to claim 1 in which the product yield is at least based on the feed.

8. Process for hydrogenating highly unstable byproduct naphtha having a bromine number of 85-135 recovered from the steam cracking of a petroleum hydrocarbon feed boiling in the range of 400l000 F. to produce a maximum quantity of ethylene comprising the steps of contacting said naphtha in a reactor with a sulfided nickel-tungsten-alurnina catalyst with a gas containing 50100% hydrogen under critical hydrogenating conditions including (1) a reactor inlet temperature of 200 to 300 F., (2) a pressure of 300 to 1200 p.s.i.g., (3) a space velocity of 0.25 to 2.0 v./hr./v., (4) a hydrogen to naphtha ratio of 500 to 2500 s.c.f./b., and recovering a stable [motor gasoline component having a bromine number of less than 85, a copper beaker gum content of less than 20 mg./ ml., and a good odor.

References Cited UNITED STATES PATENTS 2,878,179 3/1959 Hennig 208-57 2,953,519 9/1960 Bercik et a1. 208'143 3,113,096 12/1963 White 208143 3,149,180 9/1964 Platteuw et al. 260-683.65 3,310,485 3/1967 Bercik et al. 208*143 DELBERT E. GANTZ, Primary Examiner.

H. LEVINE, Assistant Examiner. 

